1. Field of the Invention
The present invention relates generally to an electrophotographic copying machine and, more particularly, to the electrophotographic copying machine comprising an image reader unit for reading an image of a document to be copied, a printer unit for the formation of an image and an image storage unit for the storage of the image.
2. Description of Related Art
In general, a digital copying machine has a capability of storing in a memory an image data read by an image sensor such as CCD and, therefore, the copying machine is capable of executing a so-called memory mode copying operation. The memory mode copying operation refers to the operation in which, in case of multiple copying, the document is read only one time and the read image data is then stored in the memory so that the image data stored is repeatedly read from the memory to form a required number of copies. As compared with an analog copying machine which operates only under a direct-coupled mode, the digital copying machine of the type referred to above is advantageous in that the number of times over which the document is read is reduced, permitting an increase in copying speed.
Also, during the memory mode copying operation, rotation of the direction of the document is turned 90 degrees while stored in the memory enables a memory sorting with no need to use any mechanical sorting machine.
Most of the copying machine have a capability of selecting a plurality of modes for making a double-sided copy from a single-sided document, a double-sided copy from a double-sided document, a single-sided copy from a double-sided document, a synthesized copy in which two documents are reproduced on a single recording paper and a combination of one of them with a multi-copy.
During the execution of any of those modes, for example, a double-sided copy mode, a recording paper having one of first and second opposite sides which has been copied must be temporarily accommodated in an intermediate tray or the like and is then turned upside down, whereupon the recording paper is supplied again to a transfer station. Also, in order to accomplish a double-sided document mode, the document, one side of which has been read, must be transported within an automatic document feeder and is then turned upside down.
In the prior art digital copying machine, during the execution of the mode in which a double-sided copy is made for each of a plurality of double-sided documents, the documents are sequentially read in the order from the first side of the first, the second side of the first, the first side of the second, the second side of the second and so on, so that the image read from the documents can be formed during the reading of the image of the next succeeding document.
Accordingly, in order for the copying of the second side of the document to be initiated subsequent to the copying of the first side of the document, each document must be turned upside down and a wait must be made until the associated recording paper is also turned upside down.
Because of this, in the prior art copying machine, the interval between the neighboring cycles of image formation tends to be lengthened and, therefore, a substantial length of time is required to complete the copying of the whole number of pages and, hence, the copying machine as a whole is susceptible to a reduced copying speed.
Also, in the digital copying machine, it has been practiced that, in order for the image data to be highly efficiently stored, the image data read is compressed to provide a code data which is in turn stored, so that, when the necessity arises, the code data is expanded at a timing different from the timing of compression to restore to the image data.
Where the memory mode copying is carried out with this type of prior art digital copying machine, after the whole number of the documents have been read and compressed and after the code data has been completely stored in the memory, the image data are sequentially read from the memory and are expanded in readiness for reproduction onto copying papers.
Also, where the multi-copy is carried under the memory mode for making a copy for each double-sided document, after the whole number of the documents have been read and subsequently stored in the memory, the image data are sequentially read from the memory and are then reproduced on copying papers.
Because of the foregoing, a prolonged length of time is required to complete the copying of the whole number of the documents, rendering the copying speed as a whole to be low.